The present invention relates to testing an analog signal.
According to the known methods the signal under test is digitized using an analog-to-digital converter and the digitized signal under test is evaluated for testing the signal under test. One problem is that the distortion in the signal under test is sometimes small compared with to components of the ideal waveform of the signal under test and thus the analog-to-digital converter has to fulfil high-performance specifications, e.g. a big dynamic range for accurate conversion, in order to allow detection of small distortions in the signal under test.
If the ideal waveform of the signal under test is a sine wave, a notch filter can be used to suppress the main component of the signal under test thus relaxing the dynamic range requirements of the analog-to-digital converter. But a real notch filter is non-ideal and will also influence the distortion components in the signal under test which are to be measured. Furthermore, for testing signals with different frequencies a programmable notch filter has to be used which is expensive.
Testing of analog signals is known from, but not restricted to, Automated Test Equipment (ATE). Integrated Circuits (IC) generally need to be tested to assure proper operation. This—in particular—is required during IC development and manufacturing. In the latter case, the ICs are usually tested before final application. During test, the IC, as device under test (DUT), is exposed to various types of stimulus signals, and its responses are measured, processed and usually compared to an expected response of a good device. Automated Test Equipment (ATE) usually performs these tasks according to a device-specific test program. Examples for ATE are the AGILENT 83000 and 93000 families of Semiconductor Test Systems of AGILENT Technologies Details of those families are also disclosed e.g. in EP-A-859318, EP-A-864977, EP-A-886214, EP-A-882991, EP-A-1092983, U.S. Pat. No. 5,499,248, U.S. Pat. No. 5,453,995.